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Merged
merged 11 commits into from
Oct 6, 2025
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[SimplifyCFG] Fold the contiguous wrapping cases into ICmp. #161000

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Pre-commit test cases
dianqk Sep 27, 2025
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[SimplifyCFG] Fold the contiguous wrapping cases into ICmp.
dianqk Sep 26, 2025
c56155d
Fix the count of pruning incoming values
dianqk Sep 27, 2025
41c4da0
[SimplifyCFG] Cases to the default destination cannot be contiguous c…
dianqk Oct 2, 2025
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Add more tests
dianqk Oct 3, 2025
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[SimplifyCFG] Improve one case
dianqk Oct 3, 2025
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Add more tests
dianqk Oct 3, 2025
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[SimplifyCFG] Use icmp eq for one case
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113 changes: 89 additions & 24 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5718,15 +5718,49 @@ bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
return Changed;
}

static bool casesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
static bool casesAreContiguous(Value *Condition,
SmallVectorImpl<ConstantInt *> &Cases,
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@antoniofrighetto antoniofrighetto Oct 3, 2025

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I think the function name would deserve an update, e.g., findContiguousCases (and maybe return a std::optional struct instead of the three values as out parameters)?

ConstantInt *&ContiguousCasesMin,
ConstantInt *&ContiguousCasesMax,
bool &IsWrapping) {
assert(Cases.size() >= 1);

array_pod_sort(Cases.begin(), Cases.end(), constantIntSortPredicate);
for (size_t I = 1, E = Cases.size(); I != E; ++I) {
if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
auto Min = Cases.back()->getValue();
auto Max = Cases.front()->getValue();
auto Offset = Max - Min;
auto ContiguousOffset = Cases.size() - 1;
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@antoniofrighetto antoniofrighetto Oct 3, 2025

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No need for auto here, having the type explicit (const APInt&, unsigned) would make the code more readable.

if (Offset == ContiguousOffset) {
ContiguousCasesMin = Cases.back();
ContiguousCasesMax = Cases.front();
return true;
}
ConstantRange CR = computeConstantRange(Condition, /*ForSigned=*/false);
// If this is a wrapping contiguous range, that is, [Min, OtherMin] +
// [OtherMax, Max] (also [OtherMax, OtherMin]), [OtherMin+1, OtherMax-1] is a
// contiguous range for the other destination. N.B. If CR is not a full range,
// Max+1 is not equal to Min. It's not continuous in arithmetic.
if (Max == CR.getUnsignedMax() && Min == CR.getUnsignedMin()) {
assert(Cases.size() >= 2);
auto *It =
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@antoniofrighetto antoniofrighetto Oct 3, 2025

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How about something as follows before the logic here?

// Find the first non-consecutive pair, and ensure this pair
// happens to be unique.

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@antoniofrighetto antoniofrighetto Oct 3, 2025

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(I meant this before the std::adjacent_find, which is not appearing)

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@dianqk dianqk Oct 4, 2025

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I think this is what you want. std::adjacent_find finds one non-consecutive pair and checks their distance to check if this pair is unique.

std::adjacent_find(Cases.begin(), Cases.end(), [](auto L, auto R) {
return L->getValue() != R->getValue() + 1;
});
if (It == Cases.end())
return false;
auto *OtherMax = *It;
auto *OtherMin = *(It + 1);
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Suggested change
auto *OtherMax = *It;
auto *OtherMin = *(It + 1);
auto [OtherMax, OtherMin] = std::make_pair(*It, *std::next(It));

if ((Max - OtherMax->getValue()) + (OtherMin->getValue() - Min) ==
Cases.size() - 2) {
ContiguousCasesMin = cast<ConstantInt>(
ConstantInt::get(OtherMin->getType(), OtherMin->getValue() + 1));
ContiguousCasesMax = cast<ConstantInt>(
ConstantInt::get(OtherMax->getType(), OtherMax->getValue() - 1));
IsWrapping = true;
return true;
}
}
return true;
return false;
}

static void createUnreachableSwitchDefault(SwitchInst *Switch,
Expand Down Expand Up @@ -5797,37 +5831,68 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
assert(!CasesA.empty() || HasDefault);

// Figure out if one of the sets of cases form a contiguous range.
SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
ConstantInt *ContiguousCasesMin = nullptr;
ConstantInt *ContiguousCasesMax = nullptr;
BasicBlock *ContiguousDest = nullptr;
BasicBlock *OtherDest = nullptr;
if (!CasesA.empty() && casesAreContiguous(CasesA)) {
ContiguousCases = &CasesA;
bool IsWrapping = false;
SmallVectorImpl<ConstantInt *> *ContiguousCases = &CasesA;
SmallVectorImpl<ConstantInt *> *OtherCases = &CasesB;

// Only one icmp is needed when there is only one case.
if (!HasDefault && CasesA.size() == 1) {
ContiguousCasesMax = CasesA[0];
ContiguousCasesMin = CasesA[0];
ContiguousDest = DestA;
OtherDest = DestB;
} else if (casesAreContiguous(CasesB)) {
ContiguousCases = &CasesB;
} else if (CasesB.size() == 1) {
ContiguousCasesMax = CasesB[0];
ContiguousCasesMin = CasesB[0];
ContiguousDest = DestB;
OtherDest = DestA;
std::swap(ContiguousCases, OtherCases);
}
// Correctness: Cases to the default destination cannot be contiguous cases.
else if (!HasDefault && !CasesA.empty() &&
casesAreContiguous(SI->getCondition(), CasesA, ContiguousCasesMin,
ContiguousCasesMax, IsWrapping)) {
ContiguousDest = DestA;
OtherDest = DestB;
} else if (casesAreContiguous(SI->getCondition(), CasesB, ContiguousCasesMin,
ContiguousCasesMax, IsWrapping)) {
ContiguousDest = DestB;
OtherDest = DestA;
std::swap(ContiguousCases, OtherCases);
} else
return false;

// Start building the compare and branch.

Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
Constant *NumCases =
ConstantInt::get(Offset->getType(), ContiguousCases->size());
if (IsWrapping) {
std::swap(ContiguousDest, OtherDest);
std::swap(ContiguousCases, OtherCases);
}

Value *Sub = SI->getCondition();
if (!Offset->isNullValue())
Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
// Start building the compare and branch.

Value *Cmp;
Constant *Offset = ConstantExpr::getNeg(ContiguousCasesMin);
Constant *NumCases = ConstantInt::get(Offset->getType(),
ContiguousCasesMax->getValue() -
ContiguousCasesMin->getValue() + 1);
BranchInst *NewBI;
if (NumCases->isOneValue()) {
assert(ContiguousCasesMax->getValue() == ContiguousCasesMin->getValue());
Value *Cmp = Builder.CreateICmpEQ(SI->getCondition(), ContiguousCasesMin);
NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
}
// If NumCases overflowed, then all possible values jump to the successor.
if (NumCases->isNullValue() && !ContiguousCases->empty())
Cmp = ConstantInt::getTrue(SI->getContext());
else
Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
else if (NumCases->isNullValue() && !ContiguousCases->empty()) {
NewBI = Builder.CreateBr(ContiguousDest);
} else {
Value *Sub = SI->getCondition();
if (!Offset->isNullValue())
Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
}

// Update weight for the newly-created conditional branch.
if (hasBranchWeightMD(*SI)) {
Expand Down Expand Up @@ -5860,7 +5925,7 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
}
for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
unsigned PreviousEdges = OtherCases->size();
if (OtherDest == SI->getDefaultDest())
++PreviousEdges;
for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
Expand Down
4 changes: 2 additions & 2 deletions llvm/test/Transforms/Coroutines/coro-catchswitch-cleanuppad.ll
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Expand Up @@ -80,8 +80,8 @@ cleanup2:
; CHECK: cleanup2.corodispatch:
; CHECK: %1 = phi i8 [ 0, %handler2 ], [ 1, %catch.dispatch.2 ]
; CHECK: %2 = cleanuppad within %h1 []
; CHECK: %switch = icmp ult i8 %1, 1
; CHECK: br i1 %switch, label %cleanup2.from.handler2, label %cleanup2.from.catch.dispatch.2
; CHECK: %3 = icmp eq i8 %1, 0
; CHECK: br i1 %3, label %cleanup2.from.handler2, label %cleanup2.from.catch.dispatch.2

; CHECK: cleanup2.from.handler2:
; CHECK: %valueB.reload = load i32, ptr %valueB.spill.addr, align 4
Expand Down
12 changes: 4 additions & 8 deletions llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
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Expand Up @@ -7,8 +7,7 @@ declare void @foo(i32)
define void @test(i1 %a) {
; CHECK-LABEL: define void @test(
; CHECK-SAME: i1 [[A:%.*]]) {
; CHECK-NEXT: [[A_OFF:%.*]] = add i1 [[A]], true
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i1 [[A_OFF]], true
; CHECK-NEXT: [[SWITCH:%.*]] = icmp eq i1 [[A]], true
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
Expand Down Expand Up @@ -209,8 +208,7 @@ define void @test5(i8 %a) {
; CHECK-SAME: i8 [[A:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[A]], 2
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[A_OFF:%.*]] = add i8 [[A]], -1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[A_OFF]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp eq i8 [[A]], 1
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
Expand Down Expand Up @@ -243,8 +241,7 @@ define void @test6(i8 %a) {
; CHECK-NEXT: [[AND:%.*]] = and i8 [[A]], -2
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[AND]], -2
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[A_OFF:%.*]] = add i8 [[A]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[A_OFF]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp eq i8 [[A]], -1
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
Expand Down Expand Up @@ -279,8 +276,7 @@ define void @test7(i8 %a) {
; CHECK-NEXT: [[AND:%.*]] = and i8 [[A]], -2
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[AND]], -2
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[A_OFF:%.*]] = add i8 [[A]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[A_OFF]], 1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp eq i8 [[A]], -1
; CHECK-NEXT: br i1 [[SWITCH]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
Expand Down
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